Development of immortalized endometrial epithelial and stromal cell lines from the mink (Mustela vison) uterus and their effects on the survival in vitro of mink blastocysts in obligate diapause.

Mink endometrial cell lines were established by stable transfection of a plasmid vector encoding the SV40 large T antigen driven by the human beta-actin promoter. A second plasmid vector, pSV2neo, was employed for selection of transfected cells. Specificity and homogeneity of consequent cell lines were evaluated by immunocytochemistry employing antibodies against cytokeratin, desmin, and vimentin. Cytokeratin was found exclusively in epithelial cells, whereas vimentin appeared primarily in stromal cells. Neither cell line showed detectable desmin activity. These cell lines along with Buffalo rat liver (BRL) cells were employed in coculture with mink embryos in obligate diapause. Mink stromal and BRL cell lines were most effective in enhancing embryo survival in vitro. The percentages of cocultured embryos that survived for 72 h or more were 65% with epithelial cells, 75% with stromal cells, 68% with the combination of stromal and epithelial cells, and 93% with BRL cells. Only 23% of the embryos cultured without cells survived beyond 48 h. Embryo growth was also observed; some embryos in coculture showed trophoblastic outgrowth and adhesion to the cell surfaces. These results demonstrate that mink embryos in obligate delay can survive and develop in culture and that coculture with uterine or BRL cells increases the length and frequency of survival.